I'm not sure, of course.
I'm thinking maybe, if a guy shows interest, and that you have a camaraderie, that you might think it's "too good to be true."
Maybe you're skeptical about a person who treats you well...for you might think there's an ulterior motive.
I've seen this happen time and again.
I also sense that you don't like it "too easy" in general---that you find if there's a "struggle" that there's more substance than when there's "not a struggle." That you feel that a man is more substantial if you have to struggle to understand him. That you also enjoy a good debate, and that you find men who don't have strong opinions to be "wishy washy."
I can't see any other reason for this. Because you seem pretty reasonable. You write well. You make sense when you write. You're just a pretty reasonable person, I have found, since I've "known" you here for about 2 1/2 years or so.